ESP32 system failure during deepsleep outcome?

[davefes]

I want to use deepsleep on a project and was hoping someone has some
real-world experience with the ESP32.

I currently used lightsleep on a ESPNow link, wake up every minute and pat
both a system WDT and a SW WDT. I now want to put the system into deepsleep
for an hour and as the units will re-boot, via a RTC alarm, any watchdogs
now seem irrelevant.

Correct me, if I have this wrong.

What will happen to an ESP32 in deepsleep if something crashes somewhere, will
it re-boot or just stop working?

[karfas]

What will happen to an ESP32 in deepsleep if something crashes somewhere, will it re-boot or just stop working?

This question is too broad. When your power supply "crashes", the ESP32 will stop working too (of course).

There are only minor differences between a hard reset and coming out of deep sleep.
In my opinion, an ESP32 not waking up from a timed deep sleep is the least thing you need to worry about when designing a high-available system.
Even that can be fixed by an external watchdog doing a reset after two hours or so - at the cost of some microamperes for the watchdog.

However, you need to ensure (by your software watchdog, perhaps) that the ESP32 really enters deep sleep after your program did it's thing.
You don't want a perfectly working ESP32 sitting there and waiting for REPL input...

[davefes]

@karfas I naively thought that there would be a power consumption cost running these four timers. When most articles state "everything is shut-down except for the RTC timer" that suggests to me that using these four timers are going to incur extra power consumption.

Heh, if I can keep the total deepsleep current under 1mA I don't need dig any deeper!

Thanks, again.

[karfas]

I have no idea how machine.Timer() came into this discussion.

@davefes: it would be "naive" to assume that additional things will be working without power consumption.

Heh, if I can keep the total deepsleep current under 1mA I don't need dig any deeper!

I'm sure this is possible, but be aware that most ESP32 development boards were not designed with "low power" in mind.
Components like the UART/USB converter, LEDs, ... might consume precious microamperes, even when the ESP32 module itself runs with less than 10 uA during deep sleep.

[davefes]

I brought it in by mentioning that my SW WDT uses machine.timer(). If machine.timer stops running in deepsleep() then this won't work.
Likewise, if machine.WDT stops running in deepsleep() then this won't work either.

I'll be able to do some tests in 2 days. All the boards I use in low-power apps have the on-board LED and 3V3 regulator removed and a jumper link put in for the CP2102 UART bridge supply.

[karfas]

If machine.timer stops running in deepsleep() then this won't work. Likewise, if machine.WDT stops running in deepsleep() then this won't work either.

You still don't realize what deep sleep is. Only some functions of the RTC module and the ULP processor are running; everything else gets no power. What should a watchdog do if a program that is not supposed to run (during deep sleep) really isn't running ?

Of course any kind of watchdog will be useful while the application runs so you can ensure the processor starts again from a clean state in case something unexpected happens.

[davefes]

You still don't realize what deep sleep is.

Yes, I will admit that I am struggling a bit here.

I know that the program does not run during light or deepsleep. I know that you can use the RTC timer to wake from deepsleep after a rough amount of time. I see that ability to wake-up again important and also thought that it might be subject to failure. I am probably confusing things by calling this ability to wake-up and start over again a sort of "watchdog".

I have some DS3231s coming, which I will set up to give one hour alarms to wake the ESP32s up from deepsleep. I need timing accuracy as I need to sync three ESP32s, ie within a few seconds.

I have read quite a few articles on watchdogs and it does get quite complex the issues that people try to cater for, ie race conditions in code and cosmic rays!

[karfas]

I see that ability to wake-up again important and also thought that it might be subject to failure.

OK, but there is very little you can do about a not working or not booting device without external supervision. Most likely, any error during boot after deep sleep will also prevent a clean boot by machine.reset() and the like.
You will have to test and trust the ESP32 wakeup functions as well as you trust the reset button, the watchdog, and machine.reset().
The DS3231 will not help much in this regard.

If it is really that important (e.g. live-saving) that the device comes out from deep sleep, you could add one or more ESP32 and work out some logic so at least one of them performs it's function.

[davefes]

The main purpose of the DS3231 is to sync wake-up times for multiple devices so that I can establish two-way communications then go to sleep for an hour.

Fortunately, this is not a life-saving situation. When I don't get an hourly update then it would mean a walk up some small hills to reset devices.

I read through several of your PRs and appreciate the level of your comments.